THC's pain-relieving mechanism involves interacting with CB1 receptors and enhancing naturally occurring endocannabinoids.

“In fact, the presence of CB1 receptors in the spinal cord largely explains the fact that THC and CBD, to some extent, although it's not very well studied, can provide some pain relief. I say some, because a lot of people perceive or believe that they experience more pain relief from cannabis than they actually do. It actually has a lot to do with a perceptual shift to basically focusing on other things, but there does seem to be some antinociceptive, meaning anti pain effects of cannabis, THC in particular, and that is exerted largely through effects on CB1 receptors in neurons of the spinal cord.”